Catalytic burner system for dpf regeneration

ABSTRACT

A system and method of effective regeneration of a diesel particulate filter used in the exhaust system of a diesel engine during low engine operating temperatures, is disclosed. Generally speaking, a catalytic burner system and method used in filter regeneration on a diesel engine comprises a burner diesel oxidation catalyst (BDOC) coupled to an exhaust flow of the diesel engine, a mixer fluidly coupled to the BDOC, a diesel oxidation catalyst (DOC) fluidly coupled to the mixer, and a diesel particulate filter (DPF) fluidly coupled to the DOC, wherein the BDOC directs the exhaust flow through the mixer, the DOC and the DPF during a regeneration cycle of the DPF under low engine temperature operating conditions.

TECHNICAL FIELD

The present system and method relate to the use of a filter for treatment of exhaust gases in a diesel engine. Specifically, the system and method relate to efficient regeneration of a diesel particulate filter under low temperature engine operation.

BACKGROUND

Diesel engines are efficient, durable and economical. Diesel exhaust, however, can harm both the environment and people. To reduce this harm, governments, such as the United States and the European Union, have proposed stricter diesel exhaust emission regulations. These environmental regulations require diesel engines to meet the same pollution emission standards as gasoline engines. Typically, to meet such regulations and standards, diesel engine systems require equipment additions and modifications.

For example, a lean burning engine provides improved fuel efficiency by operating with an amount of oxygen in excess of the amount necessary for complete combustion of the fuel. Such engines are said to run “lean” or on a “lean mixture.” However, the increase in fuel efficiency is offset by the creation of undesirable pollution emissions in the form of nitrogen oxides (NO_(x)). Nitrogen oxide emissions are regulated through regular emission testing requirements. One method used to reduce NO_(x) emissions from lean burn internal combustion engines is known as selective catalytic reduction. When used to reduce NO_(x) emissions from a diesel engine, selective catalytic reduction involves injecting atomized urea into the exhaust stream of the engine in relation to one or more selected engine

Another method for reducing NO_(x) emissions is exhaust gas recirculation (EGR), which is a technique that re-circulates a portion of an engine's exhaust gas back to the engine cylinders. Engines employing EGR recycle part of the engine exhaust back to the engine air intake. The oxygen depleted exhaust gas blends into the fresh air entering the combustion chamber. Reducing the oxygen produces a lower temperature burn, reducing NO_(x) emissions by as much as 50%. The recycled exhaust gas can then be cooled. This “cooled EGR”, can create an even greater reduction in emissions by further lowering the combustion temperatures. When used with a DPF (diesel particle filter), emissions can be reduced up to 90%.

The DPF includes a diesel oxidation catalyst (DOC), which is a ceramic material that heats up in the DPF. The filter is used to collect particulate matter from the DPF. Over time, soot and particulate matter accumulates in the DPF, which is cleaned of particulate matter at periodic intervals through a regeneration process. Regeneration is the process of removing the accumulated soot from the filter. This is done either passively (from the engine's exhaust heat in normal operation or by adding a catalyst to the filter) or actively by introducing very high heat (more than 600° C. to burn off the particulate matter) into the exhaust system. The high temperatures need to be maintained continuously from 10 up to 30 minutes for effective regeneration.

Commonly, DPF regeneration systems rely on upstream fuel injection (in-cylinder or in-exhaust) and combustion of the injected fuel in the DOC positioned between the fuel injector and the DPF to create the necessary temperature rise. However, effective DPF regeneration becomes problematic under driving conditions that produce low engine exhaust temperatures, such as observed in stop-and-go traffic. Low temperatures create few opportunities for the DOC to reach the required temperatures needed to initiate and maintain the DPF regeneration. Furthermore, active regeneration events may be interrupted if the temperature at the DOC inlet falls below the required temperature limit (250° C. to 300° C. to burn fuel), making it impossible for the DOC to support the regeneration process. Thus, there is a need for improving the light-off of the DOC during conditions when the exhaust temperature is low and transient.

In an effort the sustain the fuel combustion in the DOC for effective regeneration, the present system incorporates a burner DOC (BDOC) to direct a portion of the exhaust flow through the DOC at a low gas velocity. The optimum exhaust flow through the BDOC is estimated at 20-40% of the total flow. This desired flow is achieved by selecting a BDOC substrate material such that its flow resistance allows for only an optimum portion of the flow to enter the BDOC. Such pressure resistance may be hard to achieve, and the substrate material required for such flow resistance may be difficult to coat with catalytically active material. In addition, the inlet of the BDOC may become clogged by large solid particles, which can be formed in the exhaust pipe under certain conditions, which then carries the risk of blocking the BDOC channels, thereby increasing the pressure drop and reduced fuel combustion performance.

The present system and methods solve these and other problems in providing effective DPF regeneration under low temperature engine operation.

SUMMARY

A system and method for effective DPF regeneration under low engine operating temperatures for diesel engine is disclosed. Generally speaking, a catalytic burner system for use in regeneration of a filter on a diesel engine comprises a burner diesel oxidation catalyst (BDOC) coupled to an exhaust flow of the diesel engine, a mixer fluidly coupled to the BDOC, a diesel oxidation catalyst (DOC) fluidly coupled to the mixer, and a diesel particulate filter (DPF) fluidly coupled to the DOC, wherein the BDOC directs the exhaust flow through the mixer, the DOC and the DPF during a regeneration cycle of the DPF under low engine temperature operating conditions.

A method for regenerating a diesel engine particulate filter (DPF) during periods of low engine operating temperatures, is disclosed. The method comprises the steps of channeling a portion of exhaust flow toward a first chamber, restricting the flow velocity of the exhaust flow as it enters the chamber, expanding the flow velocity of the exhaust flow as it leaves the chamber, catalytically oxidizing the exhaust flow in a second chamber, maintaining a pre-determined regeneration temperature within the second chamber; and, regenerating the DPF.

Another method for regenerating a diesel engine particulate filter during periods of low engine operating temperatures, is disclosed. The method comprises the steps of fluidly coupling components of an exhaust gas treatment system package to an exhaust system of the diesel-engine vehicle, regulating the flow of exhaust gases through the components of the treatment system package, and maintaining a desired temperature for regeneration.

The BDOC is ideally designed to channel a portion of the exhaust flow through the system for effective filter regeneration. In one embodiment, the BDOC includes a conical collar. In alternative embodiment, the BDOC has a conical shape with a inlet orifice fluidly connected to an outlet for maintaining a lower flow velocity. In yet another embodiment, the BDOC comprises a first substrate having a plurality of wide channels and a second substrate having a plurality of narrow channels relative to the first substrate channels, wherein the second substrate is positioned downstream from the first substrate and separated by a gap.

These and other embodiments and their advantages can be more readily understood from a review of the following detailed description and the corresponding appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of a exhaust treatment system incorporating a burner diesel oxidation catalyst (BDOC);

FIG. 2 is an embodiment of a BDOC useful in the present system and method;

FIG. 3 is another embodiment of a BDOC useful in the present system and method;

FIG. 4 is yet another embodiment of a BDOC useful in the present system and method.

DETAILED DESCRIPTION

With reference to FIGS. 1-4, the DPF regeneration system is shown and consistently referenced by the number “10” throughout. The DPF regeneration system 10 is incorporated into the exhaust system of a diesel engine (not shown). In the illustrated embodiment, the system 10 is generally comprised of a first chamber or burner diesel oxidation catalyst (BDOC) 12, a mixer 14, a second chamber or diesel oxidation catalyst (DOC) 16, and a diesel particulate filter (DPF) 18. The mixer 14, the DOC 16, and DPF 18 are exhaust gas treatment structures present in most diesel exhaust gas treatment systems. Such structures will be generally referenced herein and identified in the drawing figures but, as each of these additional exhaust treatment structures is commonly understood by those skilled in the art, a detailed discussion of the operation of each will not be presented.

Referring to FIG. 1, there is shown a DPF regeneration system 10. When the DPF 18 accumulates a certain level of soot, a sensor or series of sensors (not shown) incorporated into the main control module (not shown) signal initiation of the regeneration of the filter. Complete regeneration typically requires an exhaust temperature in the range of from about 550 to about 600° C. for about a 10-30 minute interval. A typical DOC 16, which provides a means for sustaining fuel combustion in the system 10, requires incoming exhaust gas to be between 250-300° C. to effectively burn fuel and maintain enough heat to regenerate the DPF 18. During a typical regeneration cycle, super-heated exhaust is mixed with fuel and enters the system. As will be described, the first chamber or BDOC 12 provides a means for channeling a portion of the exhaust flow through the system 10. The BDOC 12 is designed to sustain the required temperature for efficient fuel combustion in the second chamber or DOC 16 as it directs a portion of the exhaust flow through the system 10 during low gas velocity. Ideally, the BDOC 12 should include the following characteristics: it should light off at approximately the same temperature, or lower than the main DOC 16, while having a higher back pressure than that of the surrounding volume, such that only a small portion of the exhaust gas flows through it, allowing a lower velocity than the main flow and resulting in stabilized fuel combustion. In addition, the BDOC 12 may be constructed of any suitable material that maintains high thermal conductivity.

Referring to FIG. 2, there is shown a first embodiment of a BDOC 12 a. In this embodiment, the BDOC includes a cone-shaped collar 20, which is positioned at an inlet side of the BDOC. Use of the collar 20, and particularly with the narrower opening 20 a of the collar 20 facing toward the exhaust stream, limits the flow of exhaust through the BDOC 12 a, resulting in stabilized fuel combustion.

Referring to FIG. 3, there is shown a second embodiment of a BDOC 12 b useful in the present system 10. In this particular embodiment, the BDOC 12 b has a conical shape, wherein the narrower opening 22 faces the incoming exhaust stream, limiting the flow of exhaust through the BDOC 12 b. The opposing wider outlet 24, connected with the remaining components of the system 10, contributes to less restriction around the BDOC 12 b, lower flow velocity and greater stability of both the exhaust flow and temperatures required for effective regeneration of the DPF 18.

Referring to FIG. 4, there is shown a third embodiment of a BDOC 12 c useful in the present system 10. In this particular embodiment, the BDCO 12 c is constructed from at least two different substrates. As shown, a first substrate 26 is ideally constructed having a plurality of wide, parallel channels 26 a, which are positioned at the inlet of the BDOC 12 c. The wide channels 26 a in the first substrate 26 prevent plugging of the inlet of the BDOC 12 c, which may happen if large particulate materials are part of the exhaust stream. A second substrate 28, positioned downstream from the first substrate 26, is ideally constructed from a plurality of narrow, parallel channels 28 a, which are narrower relative to the channels 26 a in the first substrate. The narrow channels 28 a in the second substrate 28 facilitate heat transfer. In addition, a gap 30 separates the first substrate 26 from the second substrate 28, adding turbulence and facilitating mixing of the exhaust gases and fuel between the first substrate 26 and the second substrate 28. The actual measurements of each substrate 26, 28 and the width of the gap 30 may vary depending on the specific requirements of the BDOC design used in the system 10.

Regardless of which of the three BDOC 12 a, 12 b, 12 c designs described herein, or any suitable variation thereof, is incorporated into the exhaust system, the BDOC should be constructed from a material having a high thermal conductivity, including any suitable metallic substrate (e.g., stainless steel). Use of a BDOC constructed of a high thermal conductivity material balances the heat transport process resulting in stable combustion at low inlet temperatures. The exact properties and specifications of the BDOC 12 will depend on the technical requirements of the vehicle in which it will be used. However, some general preferred properties include, but are not limited to: the flow through the BDOC 12 should be 25-30% of the total flow through the system; the diameter of the BDOC should be such that the BDOC is compatible with the DOC 16 and DPF 18 to create a uniform system and flow; and, the length of the BDOC should be such that it provides for easy packaging as the exhaust system of the vehicle.

Diesel particulate filters typically require periodic regeneration. The present system and method provides regeneration of a DPF during low engine exhaust temperatures, such as during stop-and-go driving. A method for regenerating a diesel engine particulate filter (DPF) during periods of low engine operating temperatures comprises the steps of channeling a portion of exhaust flow toward a first chamber; restricting the flow velocity of the exhaust flow as it enters the first chamber; expanding the flow velocity of the exhaust flow as it leaves the first chamber; catalytically oxidizing the exhaust flow in a second chamber; maintaining a pre-determined regeneration temperature within the second chamber; and, regenerating the DPF. The system 10 requires the first chamber or BDOC 12, which serves as the means for channeling a portion of exhaust flow. The system 10 also requires the second chamber or DOC 16, which serves as the means for maintaining a pre-determined temperature for filter regeneration at low operating temperatures. Use of the BDOC 12, having any suitable configuration for ideally channeling and restricting the flow of exhaust gases through the system, provides a method of sustaining fuel combustion and temperatures required for regeneration in the DOC resulting in effective DPF regeneration during low temperature operating conditions. 

What is claimed is:
 1. A catalytic burner system for use in regeneration of a filter in an exhaust system on a diesel engine, the burner system comprising: a burner diesel oxidation catalyst (BDOC) having an inlet for receiving an exhaust flow from the diesel engine and an outlet at an opposing end; a mixer fluidly coupled to the outlet of the BDOC; a diesel oxidation catalyst (DOC) fluidly coupled to the mixer; and, a diesel particulate filter (DPF) fluidly coupled to the DOC, wherein the BDOC channels the exhaust flow through the mixer, the DOC and the DPF during a regeneration cycle of the DPF under low engine temperature operating conditions.
 2. The system of claim 1, wherein the BDOC further includes a collar positioned at the inlet of the BDOC.
 3. The system of claim 2, wherein the collar has a conical shape including a narrower opening and a wider outlet.
 4. The system of claim 3, wherein the collar directs the exhaust flow through the BDOC at a pre-determined flow rate.
 5. The system of claim 1, wherein the BDOC has a conical shape, having a narrower inlet channeling the exhaust flow toward a wider outlet.
 6. The system of claim 1, wherein the BDOC comprises a first substrate and a second substrate, wherein the second substrate is positioned downstream from the first substrate.
 7. The system of claim 6, wherein the first substrate comprises a plurality of wider channels and the second substrate comprises of plurality of narrow channels.
 8. The system of claim 7, wherein the first substrate and the second substrate are separated by a gap, wherein the gap enhances mixing of the exhaust flow between the first substrate and the second substrate.
 9. A method for regenerating a diesel engine particulate filter (DPF) during periods of low engine operating temperatures, the method comprising the steps of: channeling a portion of exhaust flow toward a first chamber; restricting the flow velocity of the exhaust flow as it enters the chamber; expanding the flow velocity of the exhaust flow as it leaves the chamber; catalytically oxidizing the exhaust flow in a second chamber; maintaining a pre-determined regeneration temperature between the first chamber and the second chamber; and, regenerating the DPF.
 10. The method of claim 9, wherein the first chamber comprises a burner diesel oxidation catalyst (BDOC).
 11. The method of claim 9, wherein the step of restricting the flow velocity includes the first chamber comprising a BDOC having a conical shape.
 12. The method of claim 9, wherein the step of restricting the flow velocity includes the first chamber comprising a BDOC comprising a first substrate having a plurality of wide channels and a second substrate having a plurality of narrower channels.
 13. The method of claim 9, wherein the second chamber comprises a DOC.
 14. A method for regenerating a diesel engine particulate filter during periods of low engine operating temperatures, the method comprising the steps of: fluidly coupling components of an exhaust gas treatment system package to an engine exhaust system of the diesel-engine vehicle; channeling the flow of exhaust gases through the components of the treatment system package; and, maintaining a pre-determined temperature for regeneration.
 15. The method of claim 14, wherein the step of channeling the flow of exhaust gases comprises providing a burner diesel oxidation catalyst (BDOC) having a narrow inlet fluidly connected to an outlet wider relative to the inlet.
 16. The method of claim 15, wherein the BDOC further includes a conical collar positioned at the inlet of the BDOC, the conical collar restricting the flow of exhaust gases into the exhaust gas treatment system package.
 17. The method of claim 14, wherein the step of channeling the flow of exhaust gases comprises providing a burner diesel oxidation catalyst (BDOC) comprising a conical shape having a narrow inlet and a wider outlet for restricting the flow of exhaust gases into the exhaust gas treatment system.
 18. The method of claim 14, wherein the step of channeling the flow of exhaust gases comprises providing a burner diesel oxidation catalyst (BDOC) comprising a first substrate having a plurality of wide channels and a second substrate having a plurality of narrower channels, wherein the second substrate is positioned downstream from the first substrate.
 19. The method of claim 14, wherein the step of maintaining a pre-determined temperature for regeneration comprises providing a DOC.
 20. A catalytic burner system for use in regeneration of a particulate filter in an exhaust system on a diesel engine, the burner system comprising: means for channeling a portion of exhaust flow; and, means for maintaining a pre-determined temperature for filter regeneration at low operating temperatures.
 21. The catalytic burner system of claim 20, wherein the means for channeling the exhaust flow comprises a first chamber having a conical collar.
 22. The catalytic burner system of claim 20, wherein the means for channeling the exhaust flow comprises a first chamber having a conical shape with a narrow inlet and a wider outlet.
 23. The catalytic burner system of claim 20, wherein the means for channeling the exhaust flow comprises a first chamber constructed from a first substrate having a plurality of wide channels and a second substrate having a plurality of narrower channels, wherein the second substrate is positioned downstream from the first substrate.
 24. The catalytic burner system of claim 20, wherein the means for maintaining a pre-determined temperature for filter regeneration at low operating temperatures comprises a second chamber. 